1. Field of the Invention
This invention relates to methods and apparatus for displaying video pictures and video waveforms such as those of commercial television signals, for use by production or broadcasting personnel. The invention provides simultaneous display on one CRT of a television picture and the video waveform signal at one or more selected horizontal lines of the television picture, by modulation of the electron beam intensity and deflection signals. A line whose waveform is displayed graphically is highlighted in the picture, which appears on the screen adjacent the waveform.
2. Prior Art
Video signals are composed of lines and fields, a video line being one horizontal trace of the electron beam across the television screen. Electromagnetic deflection coils driven by ramp current signals from the deflection drive circuits drive the beam horizontally and vertically to define a raster, with a plurality of horizontal lines occurring during each vertical deflection ramp. A field is the required number of successive horizontal lines which fill the screen from top to bottom as the electron beam is deflected vertically, being deflected horizontally at each line between retraces. The field can be defined by two frames of interlaced horizontal lines.
In a moving picture arrangement the video information in successive video fields changes. The changes often are relatively small, but important to the video program, the changes providing the moving picture aspects of the program. It is desirable for production personnel to monitor the aspects of the video signal at selected portions of the video signal which correspond to selected areas on the screen. It may be desirable, for example, to study individual horizontal lines from one field in the video signal or from a set of fields.
Test equipment which displays a horizontal line of video waveform in a graphic format is known. An oscilloscope operable to scan at a time base corresponding to a horizontal scan line will display graphically the amplitude of the video signal over time, i.e., the video waveform. It is also known to couple an oscilloscope display to means for counting the horizontal lines following a vertical retrace, whereby a selected (counted) line of the video signal is displayed repetitively as it occurs. Such a feature is known as a "line select" feature. Typically, the operator has the option of changing the line selected from a field or set of fields for display, with the currently selected line being indicated numerically a the line count from the last vertical retrace. As the selected line is changed, either the output of the line counter or perhaps a mechanical position indicator changes correspondingly, for indicating to the operator the particular line which has been selected and is being displayed graphically.
Display of a given counted line of the television signal as described has certain problems in that the signal is repeated only at the repetition rate of the video frame, i.e., two fields or 30 times per second in an interleaved-frame scanning arrangement wherein the horizontal lines of alternate fields are placed between one another. In order to obtain sufficient brightness of the display and to prevent undue flickering, the luminosity and the persist time of the oscilloscope display must be increased substantially. This tends to decrease the precision with which the changing video information is graphically displayed.
Display of a video line selected by counting the lines following a vertical retrace also is a cumbersome matter. The line count does not relate visually to an area of the display, whereby the operator may have to find a particular line by a process of trial and error, estimating the line number of a particular desired part of the video field or homing in on a particular line by varying the selection apparatus until some known attribute appears in the displayed line. One known possibility is to blank all the lines except the selected line, however this obviously omits all of the video field information apart from the selected line. A monitor apart from the display may be needed in order to view the overall picture from which one line is selected for display on the oscilloscope graphic display. The need for both a video monitor and an oscilloscope display increases costs.
It would be desirable to provide a single display apparatus which simultaneously shows video information in a picture or monitor format and in a graphic format of amplitude vs. time. However there are conflicts due to time and space constraints. The horizontal timing of video scanning is such as to provide a relatively long trace and a very brief retrace. Assuming the same electron beam source and deflection apparatus is to be used for both forms of display, the time during which a given line of video is driving a picture display on the screen cannot be the same time during which that line is driving a graphic display. If the two formats are used alternately, then flicker and intensity problems are doubled, and in any event additional circuitry becomes necessary to vary operation of the deflection circuits such that the two display formats are separated from one another on the screen, in each case being scanned across a limited portion of the screen area during the timing of the full horizontal trace.